1. Field Of Invention
The present invention relates to an instrument used in mass spectrometry/mass spectrometry (MS/MS). More specifically, it relates to a MS/MS instrument utilizing a double focusing mass analyzer as the second mass analyzer, the analyzer having a uniform electric field and a magnetic sector.
2. Related Background Art
MS/MS is a powerful technique to achieve structural characterization of complex organic compounds. In the MS/MS method, two mass analyzers are arranged in tandem with a chamber for collision induced dissociation inserted therebetween. Precursor ions, sometimes known as parent ions, selected by the first mass analyzer dissociate into fragment ions in the chamber and the resulting fragment ions, sometimes known as daughter ions, are analyzed by the second mass analyzer.
When precursor ions dissociate into fragment ions, it is thought that all of the fragment ions travel at the same velocity as the precursor ions. For this reason, the energies of the fragment ions lie in a wide range from the energy of the precursor to zero, corresponding to their masses.
Heretofore, various mass analyzers, such as a quadrupole analyzer, electric sector, magnetic sector, etc. have been used as the second mass analyzer of the MS/MS instrument. However, to obtain mass spectra of fragment ions with high resolution, it is required to use a double focusing mass analyzer as the second mass analyzer. When a conventional Neir-Johnson type double focusing mass analyzer having an electric sector (E) and a magnetic sector (B) is used as the second mass analyzer, the magnetic sector is scanned to obtain a fragment-ion spectrum. In such scanning-type mass analyzers, at every instant, a small part of the fragment ions can pass through both sectors and impinge on an ion detector, the greatest part of the fragment ions being lost. This leads to a deterioration in the sensitivity. Hence, there is a limit to enhancement of the sensitivity. Furthermore, since energies of fragment ions lie within a wide range, a complex scan method, namely a linked scan method, wherein both sectors E and B are varied in an interrelated manner, must be adopted.
To increase sensitivity, a simultaneous ion detection technique is advantageous as proposed by J. S. Cottrell and S. Evans (Analytical Chemistry, 59 (1987) 1990). However, a conventional Mattaugh-Herzog type double focusing mass analyzer for simultaneous detection is not capable of simultaneous detection over a wide mass range, because only fragment ions having energies lying within about 5% of the energy of precursors ions can pass through the electric sector and only a small part of fragment ion spectrum can be obtained at one measurement.